Something strange I heard almost 10 years ago

[AnyHuman]

Once in late December 2012 for a couple days, I heard an FM translator's audio making squeaking noises... It was playing Spanish Christian music, and the squeaking seemed to be most prevalent during the louder passages of songs. I found the stream online, and it too was squeaking. Different squeaks were at different pitches, like several moving parts needed some WD40 or something. I kid you not, I ain't making this up. Now that's odd!

It eventually went dead air, and several days later came back with normal-sounding audio. But I've never heard a processor or transmitter make those types of squeaky gate noises on the air. LOL anyone know what could have been causing it? I imagine the squeaking was unbareably loud in the transmitter room or studio to the naked ear without a radio.

 

[Kelly A]

anyone know what could have been causing it? I imagine the squeaking was unbareably loud in the transmitter room or studio to the naked ear without a radio.

Probably the audio level being fed to the digital encoder was excessive, causing the codec to clip. The chirps/squeaks you heard were the peaks overloading the encoder input.

 

[mpxbroadcast]

Once in late December 2012 for a couple days, I heard an FM translator's audio making squeaking noises... It was playing Spanish Christian music, and the squeaking seemed to be most prevalent during the louder passages of songs. I found the stream online, and it too was squeaking. Different squeaks were at different pitches, like several moving parts needed some WD40 or something. I kid you not, I ain't making this up. Now that's odd!

It eventually went dead air, and several days later came back with normal-sounding audio. But I've never heard a processor or transmitter make those types of squeaky gate noises on the air. LOL anyone know what could have been causing it? I imagine the squeaking was unbareably loud in the transmitter room or studio to the naked ear without a radio.

I heard this several times on different stations. Even on Analog TV. Maybe some audio circuit going to heaven? I know some transmitters who does this with bad grounding or danified power supplies with noise from the own transmitter going into audio modulator.

 

[kevtronics]

Maybe a faulty PPM encoder?

 

[Kelly A]

Or a Magnavox AM stereo exciter?

 

[davideduardo]

Maybe a faulty PPM encoder?

PPM encoding is a digital burst. Sounds like a data transmission but in tiny pieces, up to 12 times a minute. Let's ask Kelly what he has observed, but to me it sounds a bit like the old synchronization handshake of a dialup AOL connection.

 

[davideduardo]

Or a Magnavox AM stereo exciter?

... can't be that bad!

 

[Kelly A]

Let's ask Kelly what he has observed, but to me it sounds a bit like the old synchronization handshake of a dialup AOL connection.

That's a good description David, but I think it's even more subtle sounding than that.

I've never been a fan of Voltaire, but Telos makes the TVC15, (nod to David Bowie) which actually is a fantastic way to monitor Nielsen watermarking. If you have the time, check out the manual: https://www.telosalliance.com/uploa...on and User’s Guide-Version 2.0_C19214010.pdf
It shows how the TVC15 measures and displays live graphically, the Nielsen watermarking, and what all the data timing means.
When I've used the device, I've found it interesting how the watermarking data stops during pauses, and many times during talk passages. Same goes with violin solos. For some reason the Nielsen encoder thinks violin is speech, so it stops encoding.

 

[semoochie]

If I may borrow this thread for a moment, when I was growing up, the Top 40 station would frequently pop off the air for about a second and then pop back on with a somewhat "explosive" sound! Someone once said it was "exceeding the limiter". Does that sound right or was it something else?

 

[Kelly A]

If I may borrow this thread for a moment, when I was growing up, the Top 40 station would frequently pop off the air for about a second and then pop back on with a somewhat "explosive" sound! Someone once said it was "exceeding the limiter". Does that sound right or was it something else?

Depending on the situation, it could be a lot of different things. Some stations used to use single wideband limiters that when over-driven, could indeed make sounds like a distorted car crash. There were some stations using Collins FM exciters with built in stereo generator cards. These trash buckets were known for having severe 15kHz LPF 'filter ring', If you hit them with enough high frequencies above 13kHz, they would generate enough harmonics that the modulator section in the exciter would make an explosive gunshot sound on peaks.
My favorite was the old Harris THE1 exciters. If you hit them hard enough with a subharmonic peak, the oscillator would unlock, and the exciter would mute just after the station suddenly went off frequency.

 

[davideduardo]

That's a good description David, but I think it's even more subtle sounding than that.

I've never been a fan of Voltaire, but Telos makes the TVC15, (nod to David Bowie) which actually is a fantastic way to monitor Nielsen watermarking. If you have the time, check out the manual: https://www.telosalliance.com/uploads/25-Seven/TVC-15/TVC-15 Installation and User’s Guide-Version 2.0_C19214010.pdf
It shows how the TVC15 measures and displays live graphically, the Nielsen watermarking, and what all the data timing means.
When I've used the device, I've found it interesting how the watermarking data stops during pauses, and many times during talk passages. Same goes with violin solos. For some reason the Nielsen encoder thinks violin is speech, so it stops encoding.

It's that none of the set of potential insertion frequencies appears to match much of the range of a violin. A limitation on PPM insertion is the set of frequencies the PPM encoder is set to use as masks for the PPM watermark. And speech is often not dense or continuous enough for the length of the watermark.

 

[semoochie]

Depending on the situation, it could be a lot of different things. Some stations used to use single wideband limiters that when over-driven, could indeed make sounds like a distorted car crash. There were some stations using Collins FM exciters with built in stereo generator cards. These trash buckets were known for having severe 15kHz LPF 'filter ring', If you hit them with enough high frequencies above 13kHz, they would generate enough harmonics that the modulator section in the exciter would make an explosive gunshot sound on peaks.
My favorite was the old Harris THE1 exciters. If you hit them hard enough with a subharmonic peak, the oscillator would unlock, and the exciter would mute just after the station suddenly went off frequency.

Thanks, Kelly! This is when I was growing up so we're talking about AM. It looks like I was on the right track. Thanks again!

 

[Kelly A]

Thanks, Kelly! This is when I was growing up so we're talking about AM. It looks like I was on the right track. Thanks again!

Really the same goes; but generally that crashing sound occurred on AM when the audio caused envelope closure to exceed 100% negative modulation.

 

[Kelly A]

It's that none of the set of potential insertion frequencies appears to match much of the range of a violin. A limitation on PPM insertion is the set of frequencies the PPM encoder is set to use as masks for the PPM watermark. And speech is often not dense or continuous enough for the length of the watermark.

And what I noted from measuring around the market with the TVC15, was that, watermarking stopped during long talk periods. Not that I would, but if I were programming a N/T or S/T station, I'd be concerned about long gaps of no-encoding except when backed with music beds or when spots and promos ran. Depending on the format, that could make for long stretches of not getting credit for quarter hour(s).

 

[rfburns]

Once in late December 2012 for a couple days, I heard an FM translator's audio making squeaking noises... It was playing Spanish Christian music, and the squeaking seemed to be most prevalent during the louder passages of songs. I found the stream online, and it too was squeaking. Different squeaks were at different pitches, like several moving parts needed some WD40 or something. I kid you not, I ain't making this up. Now that's odd!

It eventually went dead air, and several days later came back with normal-sounding audio. But I've never heard a processor or transmitter make those types of squeaky gate noises on the air. LOL anyone know what could have been causing it? I imagine the squeaking was unbareably loud in the transmitter room or studio to the naked ear without a radio.

If they were receiving their audio via satellite, it could have been marginal satellite reception. Receiver or LNB started going bad then failed completely.

 

[awsherrill]

I take care of a fleet of translators which (mostly) use the same model 300-watt transmitter, from a well-regarded manufacturer, using a built-in audio processing card from another well-regarded vendor.

A few months ago I noticed that the off-air signal from one of these translators had audio artifacts similar to the ones described by the OP. Cycled power on the transmitter and the problem was resolved.